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Other examples of atoms include x, blue, 'Taco', and 'some atom'. Numbers can be floats or integers. Many Prolog implementations also provide unbounded integers and rational numbers. Variables are denoted by a string consisting of letters, numbers and underscore characters, and beginning with an upper-case letter or underscore. Variables ...
Prolog is a logic programming language that has its origins in artificial intelligence, automated theorem proving and computational linguistics. [1] [2] [3]Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is intended primarily as a declarative programming language: the program is a set of facts and rules, which define relations.
Prolog implementations usually omit the occurs check for reasons of efficiency, which can lead to circular data structures and looping. By not performing the occurs check, the worst case complexity of unifying a term with term is reduced in many cases from (() + ()) to (((), ())); in the particular, frequent case of variable-term unifications, runtime shrinks to ().
For example, the function, mother(X) = Y, (every X has only one mother Y) can be represented by the relation mother(X, Y). In this respect, logic programs are similar to relational databases, which also represent functions as relations. Compared with relational syntax, functional syntax is more compact for nested functions.
This is called a green cut operator.The ! tells the interpreter to stop looking for alternatives; however, if gotmoney(X) fails it will check the second rule. Although checking for gotmoney(X) in the second rule may appear redundant since Prolog's appearance is dependent on gotmoney(X) failing before, otherwise the second rule would not be evaluated in the first place.
Using Prolog's notation for lists, a singleton list prefix P = [H] can be seen as the difference between [H|X] and X, and thus represented with the pair ([H|X],X), for instance. Saying that P is the difference between A and B is the same as saying that append(P,B,A) holds. Or in the case of the previous example, append([H],X,[H|X]).
Each such rule can be read as an implication: … meaning "If each is true, then is true". Logic programs compute the set of facts that are implied by their rules. Many implementations of Datalog, Prolog, and related languages add procedural features such as Prolog's cut operator or extra-logical features such as a foreign function interface.
In Prolog, symbols (or atoms) are the main ... These three sentences use symbols (father, zeus, hermes, perseus and sibling) and some abstract variables (X, Y and Z). ...